1. Field of the Invention
This invention relates an automatic chemical analyzer used in the field of medical examination and, more particularly, to improvements in the distribution nozzle apparatus in the automatic chemical analyzer.
2. Description of the Related Art
Recently, various medical examinations, e.g., examinations of the blood and urine are indispensable for medical diagnosis, and automatic chemical analyzers are used for these examinations. In an automatic chemical analyzer, a sample of blood or the like is distributed in reaction cells capable of movement in a temperature-maintained reaction tank by a sample distribution nozzle apparatus, and also a reagent for reaction is distributed to the reaction cells containing the sample by a reagent distribution nozzle apparatus. The sample and reagent are reacted for a predetermined period of time in each reaction cell held in a temperature-maintained state. Subsequently, the light transmittivity or absorbance of the liquid under examination obtained after the reaction is measured by an optical measuring system. The absorbance thus measured is analyzed for examination of the sample.
In a usual distribution nozzle apparatus, e.g., a reagent distribution nozzle apparatus, assembled in such an automatic chemical analyzer, an arm is supported for revolution on a shaft provided at the center of an annular array of a plurality of reagent containers, and a distribution nozzle is secured to a free end of the arm. In a distributing operation of such a distribution nozzle apparatus, the distribution nozzle is introduced into a specified reagent container to withdraw a predetermined quantity of reagent therefrom, and then it is retreated from the reagent container and transferred along an orbit extending above the reagent container array to a position above a specified reaction cell for distributing a predetermined quantity of reagent to the reaction cell.
In such a distribution nozzle apparatus, during the reagent withdrawing operation a small quantity of reagent attached to the nozzle end drops during revolution of the nozzle. The dropping reagent is frequently liable to enter a different reagent container to cause mixture of different reagents. For this reason, in the prior art distribution nozzle apparatus a shutter is provided in the vicinity of each reagent container such that the opening of the reagent container is closed by the shutter. When and only when withdrawing a particular reagent from a specified reagent container, the associated shutter is retreated to open the opening of the reagent container to introduce the nozzle thereinto. When the particular reagent is withdrawn by the nozzle and it is ready to cause revolution of the arm, the openings of all the reagent containers are closed by the respective shutters, and the distribution nozzle having withdrawn the reagent is revolved above the shutters toward the reaction cell. In such a distribution nozzle apparatus with the shutters, if a slight quantity of reagent attached to the nozzle at the time of the reagent withdrawal drops during the nozzle revolution, it falls on a shutter and never enters any reagent container. Thus, it is possible to avoid occasional mixture of different reagents.
With such distribution nozzle apparatus with the shutters provided for prevention of the mixing of different reagents, the shutters are each provided in the vicinity of each reagent container and are required to be operated in a predetermined timed relation to the operation of the distribution nozzle. Therefore, the construction of the distribution nozzle apparatus inevitably becomes complicated and elaborate. Besides, there is a possibility that a chemical falling on a shutter enters a mechanical part thereof and then crystallizes, thus causing an erroneous operation. In order to maintain the accuracy of the distribution nozzle apparatus, the operation of cleaning the shutters is indispensable, and a design of apparatus giving consideration to the maintenance is required. Further, the maintenance itself is a considerable burden to the operator. The above problems are also presented in case of a sample distribution apparatus which is used for a sample-distributing operation.